Build a multi-tasking OS kernel for ARM from scratch

Prerequisites

• QEMU with an STM32 microcontroller implementation
  • Build instructions

./configure --disable-werror --enable-debug \
    --target-list="arm-softmmu" \
    --extra-cflags=-DSTM32_UART_NO_BAUD_DELAY \
    --extra-cflags=-DSTM32_UART_ENABLE_OVERRUN \
    --disable-gtk
make

• GNU Toolchain for ARM
• Set $PATH accordingly

Steps

• 00-Semihosting
  • Minimal semihosted ARM Cortex-M "Hello World"
• 01a-HelloWorld
  • Enable STM32 USART to print trivial greetings
• 01b-HelloWorld
  • Almost identical to the previous one but improved startup routines
• 02-ContextSwitch-1
  • Basic switch between user and kernel mode
• 03-ContextSwitch-2
  • system call is introduced as an effective method to return to kernel
• 04-Multitasking
  • Two user tasks are interatively switching
• 05-TimerInterrupt
  • Enable SysTick for future scheduler implementation
• 06-Preemptive
  • Basic preemptive scheduling
• 07-Threads
  • Implement user-level threads
• 08-CMSIS
  • Illustrate hardware abstraction layer (HAL) by introducing CMSIS
  • Both emulator (based on stm32-p103) and real device (STM32F429i discovery) are supported.
• 09a-dueOS
  • Arduino Due
• 09b-PSoC
  • PSoC
• 10-mOS
  • mbed
  • K64F
  • Bootloader
• 11a-RPi3
  • Raspberry Pi 3 with arm64
• 11b-iPod
  • iPod
• 12-m1n1
  • MacBook Air M1

Building and Verification

• Changes the current working directory to the specified one and then

make
make qemu

Guide to Hacking 08-CMSIS

08-CMSIS implements preemptive round-robin scheduling with user-level threads for STM32F429i-Discovery (real device) and STM32-P103 (qemu).

Get the dependencies:

git submodule init
git submodule update

Install additional utilities:

• If you would like to verify the kernel on STM32F29i-Discovery, you should install:
  • st-link or OpenOCD
  • NeoCon or screen

Support Devices:

• STM32F429i-Discovery
  • Details in Chinese by NCKU
  • STM32F429i-Discovery uses USART1(Tx=PA9,Rx=PA10,baud rate=115200) as default serial port here.
    • You would need a terminal emulator, such as screen
      • Installation on Ubuntu / Debian based systems: sudo apt-get install screen
      • Then, attach the device file where a serial to USB converter is attached: screen /dev/ttyUSB0 115200 8n1
      • Once you want to quit screen, press: Ctrl-a then k
• K64F
• Raspberry Pi
• Arduino Due
• MacBook Air M1

Available commands:

Overall

• make all
  • Build all target's bin,elf,objdump files in the "release" directory.
  • NOTE: make doe NOT equal to make all here because Makefile uses eval for targets.
• make clean
  • Remove the entire "release" directory.

STM32-P103(QEMU)

• make p103 or make target PLAT=p103
  • Build "p103.bin"
• make qemu
  • Build "p103.bin" and run QEMU automatically.
• make qemu_GDBstub
  • Build "p103.bin" and run QEMU with GDB stub and wait for remote GDB automatically.
• make qemu_GDBconnect
  • Open remote GDB to connect to the QEMU GDB stub with port:1234 (the default port).

STM32F429i-Discovery(physical device)

• make f429disco or make target PLAT=f429disco
  • Build "f429disco.bin"
• make st-flash
  • Build "f429disco.bin" and flash the binary into STM32F429 with st-link.
• make st-erase
  • Sometimes, STM32F429i-Discovery will not be able to flash new binary file, then you will need to erase flash memory with st-link.
  • Erase the entire flash on STM32F429.
• make gdb_ST-UTIL
  • Using GDB with ST-LINK on STM32F429.
  • Remember to open another terminal,and type "st-util" to open "STLINK GDB Server"

Directory Tree:

• core
  • Hardware independent source and header files.
• platform
  • Hardware dependent source and header files.
• cmsis
  • With cmsis,porting would be much easier!
• release
  • This directory will be created after "Target" in Makefile is called.
  • Containing the elf,bin,objdump files in corresponding directory.
  • make clean will remove the entire directory,do not put personal files inside it!

Porting Guide:

You should know what CMSIS is and why it saves us a lot of efforts.

cmsis is a submodule from TibaChang/cmsis, maintained by Jia-Rung Chang.

The full project can be divided into two layer:

• hardware-dependent part (HAL)
  • "platform" directory
• hardware-indepentent part
  • "core" directory

Licensing

armOS is freely redistributable under the two-clause BSD License. Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.

Reference

• Baking Pi – Operating Systems Development
• OSDev - Raspberry Pi Bare Bones